1. Field of the Invention
This invention relates to an indicating apparatus and method of manufacture. More particularly, this invention relates to devices for indicating a change in condition by producing a color change and methods of manufacture therefor.
2. Description of the Related Art
In the preparation and storage of foodstuffs, both raw and cooked, it is desirable to have some manner of indicating whether frozen items have previously been thawed. This is true in both home and commercial (such as a grocery store, supermarket, or restaurant) settings. Such information is useful from health, safety, and nutritional standpoints.
In the healthcare industry, it is well known that some vaccines, blood, various medications, etc. are temperature-sensitive. Because such materials may not function properly if frozen and then thawed, it is not only desirable but also essential to know whether these materials have been previously frozen. Similarly, it would be very beneficial to know whether material, which is stored frozen, is allowed to thaw and subsequently is refrozen. Furthermore, it would be very beneficial to know whether material has been cooled below and then heated above a threshold temperature other than the freezing temperature (i.e., above or below the freezing temperature).
It is also desirable in the foodstuff, medical, and other industries to know whether material has been raised above a certain temperature. For example, some vaccines are known to not function properly if stored above a certain temperature. Thus, it would be beneficial to know whether stored material has previously been heated above a predetermined temperature.
Maximum-minimum thermometers may be used to indicate the range of temperatures to which an item has been exposed. However, the use of such apparatus with every item in a frozen food department of a grocery store or supermarket, or with every container of vaccine, blood, drug, or other heat fragile item, is both impracticable and prohibitively costly.
Freeze-thaw indicators are known. For example, the Applicant's previous patent, U.S. Pat. No. 4,163,427, which is incorporated by reference herein in its entirety, discloses an apparatus in which melting ice is used to activate a dye formation in producing a color indication of thawing. The present invention uses a pigment rather than a dye to indicate a transition over the threshold temperature. The use of a pigment allows for a greater clarity of indication, a reduced chance of error, and a reduction in manufacturing costs.
Another known device is marketed under the name “ColdMark Freeze Indicators.” This device comprises three liquids that provide a color change upon extended exposure below a certain temperature and another color change upon extended exposure above the temperature. However, this device is much larger than, and much more expensive than, the device of the present invention.